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scottjm
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[*] posted on 29-6-2013 at 21:15
Ostwald process


I did a search on this topic, and came up with few results that were useful. I have a few questions; Has anyone attempted to do this reaction in a home lab with any success? Will a pure platinum catalyst work, or does it have to have rhodium? I am looking at getting some platinum wire that is a 7:3 alloy of platinum and rhodium. What kind of material should the reaction vessel be made of? What would be the best way to limit the secondary reaction of ammonia, and nitrous into nitrogen, and water?

Here is what I was thinking of doing. I don't think it is a very good plan, but it's the best on a have so far. I was thinking of taking a beer keg, and modifying it a bit. They are made of stainless, and can hold up too 200psi. I was thinking of cutting holes in the top of the keg, and tapping that. Then installing a pressure gauge into one of them, a thermometer in to another, then two modified spark plugs to carry the electricity. On the side I would install a glass or quarts viewing window.

The spark plugs would be hooked up to a spiral of platinum wire. The spark plugs would prevent the current from shorting out on the stainless body of the keg. A current would be passed through the wire,in turn heating it up. The standard ports on the keg could be used to supply the ammonia, and oxygen. The pressure gauges would allow you to add the gasses in the ideal ratios. Again the standard gas ports on the keg would allow you to tap off the NO2 gas to be bubbled through water, or H2O2.

Tell me what you think, criticism wanted.

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[*] posted on 29-6-2013 at 22:08


while I don't have the threads handy, yes it has been tried and posted here on scimad. Granted I could be very wrong but from what I can recall the general consensus is that it is impractical for us small timers. as for pressurizing it I dunno about that. I've seen red hot Pt wire loops immersed in ammonia vapor and red NO2 came off just fine, it even manage to keep itself hot for a time. I'd rather the other members chime in but if it was me I'd be looking for other ways to make HNO3. I couldn't rule out corrosion of the gauges, taps and other parts either



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[*] posted on 30-6-2013 at 05:37


Quote: Originally posted by scottjm  
I did a search on this topic, and came up with few results that were useful. I have a few questions; Has anyone attempted to do this reaction in a home lab with any success?


Use the search facility. Member 'plante1999' did some good work on this here:

http://www.sciencemadness.org/talk/viewthread.php?tid=23320&...

[Edited on 30-6-2013 by blogfast25]




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testimento
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[*] posted on 30-6-2013 at 13:18


I was thinking of making 10 bar stainess steel device and weld a catalyst device from a car to it and wrap resistance wire around it and some insulation to get it to 900C. In one pot I put urea and naoh solution, second pot is only for NO to NO2 reaction and the third is filled with water to gather the HNO3. Air is pumped in the ammonia pot and the pot is heated slightly and a ball valve is opened a little on the water pot so the gases will flow through the catalyst and turn into NO and H2O and then oxidize again to NO2 and then bubbled through water to get HNO3. Thats my idea of ostwald.
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[*] posted on 30-6-2013 at 13:34


Catalytic converters for cars are designed to reduce NOx to N2, so your idea won't work as you've described it.
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testimento
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[*] posted on 30-6-2013 at 14:15


If they consist platinum group metals, which they do, they will work for ostwald too.

Please note that the ostwald reaction itself contains a risk of unwanted side reaction which turns the NOx into N2 and oxygen. This unwanted reaction is minimized by passing the gases fast enough so they will only catalyze once from ammonia to NO and water.

[Edited on 30-6-2013 by testimento]

[Edited on 30-6-2013 by testimento]
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plante1999
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[*] posted on 30-6-2013 at 14:41


Quote: Originally posted by testimento  
If they consist platinum group metals, which they do, they will work for ostwald too.

Please note that the ostwald reaction itself contains a risk of unwanted side reaction which turns the NOx into N2 and oxygen. This unwanted reaction is minimized by passing the gases fast enough so they will only catalyze once from ammonia to NO and water.

[Edited on 30-6-2013 by testimento]



[Edited on 30-6-2013 by testimento]


I will tell you something ok? I worked on such a project for literally hundreds of hours, and even have a fucking mark on my face of the success. First The sides reaction make WATER and nitrogen due to ammonia reduction of nitrogen oxides which happen to be catalysed by many metals including iron, copper, chromium, and nickel. Catalytic converter are DESIGNED to reduce nitrogen oxide to nitrogen, the same unwanted side reaction. Even if NOx are made, they will be reduced.

Second point, someday you will need to listen to experienced member, or you might have bad surprises. Keep doing what you like and you may lose cash, an harm or worst, not that I mind much, chemistry is not something to be based on speculation. Go on a alchemy forum, much more your place.

[Edited on 30-6-2013 by plante1999]




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[*] posted on 30-6-2013 at 15:26


There are some other obscure ways to oxidize ammonia at room temperature. It may not be practical, but it is possible.
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scottjm
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[*] posted on 30-6-2013 at 16:07


Will the 304 stainless corrode from the NO2? I think that it should be fine from the NH3, and the O2 will have no effect on the stainless. If it is then I think I found I way that I could get this reaction to work. Does anybody know if pure platinum will work, or if i need it to have some rhodium to get any kind of efficiency. I can find platinum gauze that will work better then platinum wire, but I can't find any alloyed platinum gauze.
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plante1999
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[*] posted on 30-6-2013 at 16:09


Pure platinum work.



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scottjm
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[*] posted on 30-6-2013 at 21:16


Quote: Originally posted by plante1999  
Pure platinum work.

Will my efficiency suffer? Do you know how the 304 stainless will fair as far as corrosion?
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[*] posted on 1-7-2013 at 02:17


Lot's of other materials work.
I got it working with copper wire, but the problem was that the copper melted quickly from the heat of the reaction unless the stream of ammonia was carefully controlled.




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plante1999
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[*] posted on 1-7-2013 at 11:58


Quote: Originally posted by scottjm  
Quote: Originally posted by plante1999  
Pure platinum work.

Will my efficiency suffer? Do you know how the 304 stainless will fair as far as corrosion?


Yes it will, but quartz or ceramic is recommended for the catalyst part of the reactor. The rest can be made of stainless. The efficiency will even be better but the catalyst degradation will be faster, on an small scale, that is too slow to be a real problem.




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scottjm
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[*] posted on 1-7-2013 at 13:27


Quote: Originally posted by plante1999  

Yes it will, but quartz or ceramic is recommended for the catalyst part of the reactor. The rest can be made of stainless. The efficiency will even be better but the catalyst degradation will be faster, on an small scale, that is too slow to be a real problem.


Thank you

[edit: fixed nested quotes]

[Edited on 7/6/13 by bfesser]
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[*] posted on 3-7-2013 at 22:21


Quote: Originally posted by phlogiston  
Lot's of other materials work.
I got it working with copper wire, but the problem was that the copper melted quickly from the heat of the reaction unless the stream of ammonia was carefully controlled.


Could you make a large surface area copper and induce a smaller flow rate, or even use copper piping and push coolrant air or even water through them to reduce the temp, or would it lower it too much?

Any catalyst other than platinum would suit perfectly. Platinum is good other than by the price, and all Pt for sale at ebay is at least 4-8X higher than the market price and I just dont happen to have the method or will to wander through all that to electroplate stuff with it.

[Edited on 4-7-2013 by testimento]
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plante1999
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[*] posted on 4-7-2013 at 03:15


I tested many supposedly effective catalyst, and by very far, platinum is the best



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[*] posted on 5-7-2013 at 08:08


I have been reading this and other forum posts on the Ostwald process, and I have some questions.

1. I gather from the posts that the best catalyst for oxidizing ammonia to nitrogen oxides is platinum with 10% rhodium. Is the 10% rhodium essential? (There are platinum wires advertised on ebay, and some with 30% rhodium; it makes me wonder if 30% rhodium is better than pure platinum. However, I have no plans to make a pressurized reactor, as plante1999 has done, so for now it's just academic.)

2. There was some inconclusive discussion above about catalytic converters in automobiles. Surely their purpose is to reduce nitrogen oxides to nitrogen, an unwanted side reaction as far as the Ostwald process is concerned. But can the catalysts in catalytic converters also be used to oxidize ammonia to nitrogen oxides? (Perhaps under different physical conditions or something.) The point being that catalytic converters are easy to get, and the catalysts in them are designed to operate as catalysts. Perhaps they could be useful to the amateur chemist?

3. What causes poisoning of platinum catalysts, and how easy is it to reverse? (E.g., can it be reversed just by heating the catalyst, or treating it with some reagent?)

Thanks!





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[*] posted on 5-7-2013 at 08:13


Sorry, I thought of another question.

4. What limits the concentration of nitric acid that can be obtained by reacting NO2 with water? The references all say that only dilute acid is produced this way, and it must be distilled to obtain the more concentrated azeotrope.





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scottjm
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[*] posted on 5-7-2013 at 09:14


Quote: Originally posted by annaandherdad  
I have been reading this and other forum posts on the Ostwald process, and I have some questions.

1. I gather from the posts that the best catalyst for oxidizing ammonia to nitrogen oxides is platinum with 10% rhodium. Is the 10% rhodium essential? (There are platinum wires advertised on ebay, and some with 30% rhodium; it makes me wonder if 30% rhodium is better than pure platinum. However, I have no plans to make a pressurized reactor, as plante1999 has done, so for now it's just academic.)

plante1999 has already answered that question. Pure platinum works better then alloyed platinum, but does not last as long.

2. There was some inconclusive discussion above about catalytic converters in automobiles. Surely their purpose is to reduce nitrogen oxides to nitrogen, an unwanted side reaction as far as the Ostwald process is concerned. But can the catalysts in catalytic converters also be used to oxidize ammonia to nitrogen oxides? (Perhaps under different physical conditions or something.) The point being that catalytic converters are easy to get, and the catalysts in them are designed to operate as catalysts. Perhaps they could be useful to the amateur chemist?

Again why don't you read this thread before asking questions? plante1999 has already been nice enough to answer this question. They do not work.

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annaandherdad
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[*] posted on 5-7-2013 at 11:12


I read the entire post, plus some other SM posts on the same subject, plus some outside sources. My first question is similar to the one you posed, but it was not answered by plante. All the references I've seen say that industrially a platinum-rhodium catalyst is used. Wikipedia says that the rhodium should be 10% . Plante says he tried a lot of catalysts, and platinum works best; but he did not answer your question or mine, which is how important the rhodium is, or how important the percentage of rhodium is. I'd still like to know.

As for my question 2, again, I did read the entire post, and, as I said, the discussion on this point was inconclusive. Plante pointed out that catalytic converters are designed to convert NOx to N2; but he didn't say he had tried them, and in any case, my question still remains, can the catalysts in a catalytic converter be used to make NOx from ammonia, perhaps under different physical conditions; and, more generally, might those catalysts be useful in other ways to amateur chemists?






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scottjm
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[*] posted on 5-7-2013 at 13:26


Quote: Originally posted by annaandherdad  
I read the entire post, plus some other SM posts on the same subject, plus some outside sources. My first question is similar to the one you posed, but it was not answered by plante. All the references I've seen say that industrially a platinum-rhodium catalyst is used. Wikipedia says that the rhodium should be 10% . Plante says he tried a lot of catalysts, and platinum works best; but he did not answer your question or mine, which is how important the rhodium is, or how important the percentage of rhodium is. I'd still like to know.
Either you are really bad at reading, or you don't know how to properly stage a question. There is no importance of the rhodium for hobbyist. It decreases the efficiency of the reaction, but increases the life span of your catalyst. Unless you are planning on running you reaction hundreds or possibly thousands of times it is better to just get pure platinum.
As for my question 2, again, I did read the entire post, and, as I said, the discussion on this point was inconclusive. Plante pointed out that catalytic converters are designed to convert NOx to N2; but he didn't say he had tried them, and in any case, my question still remains, can the catalysts in a catalytic converter be used to make NOx from ammonia, perhaps under different physical conditions; and, more generally, might those catalysts be useful in other ways to amateur chemists?

If you are doing this purely for academics why do you get so stuck up on catalytic converters? Under some circumstance you might be able to get some kind of results, but the way I see it it is not worth it. As you probable know plante1999 used platinum clad asbestos. I think i will use titanium media that is clad in platinum. So the price is not much different, but you can avoid a lot of headache and wasted reagents.
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[*] posted on 9-7-2013 at 19:16


I have reason to believe that car catalytic converter will not work for amateur ostwald for the simple reason of over-capacity.

Ordinary cat has surface area of excess of 10 000 square meters. They are designed to process several liters of gases per second. This would put any amateur-scale ostwald process in major trouble and give nothing but pure nitrogen and water. It would give you NO for sure, if you were able to push 5-10 liters of ammonia-air mixture through it every second, which accords to at least 3-5 grams of ammonia. Easy to achieve if you'need to make several liters of nitric in an hour in large batch process for some purpose, but the larger problem may arise from the all-stainless middle chamber where the NO is expected to be cooled and reacted with the oxygen to form the NO2 that can be solved in water to make nitric acid.

So, either you'gonna push your propane burner and air compressor to its limits and find a 500-liter container for middle chamber, or then you can happily go with that small ebay Pt-coated titanium mesh catalyst for your amateur testings. One could, maybe, cut the cat apart and insert some adjuster that one can adjust the effective layers available for catalyst and optimize the flow speed for it.
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[*] posted on 6-2-2014 at 12:21


I was thinking of getting my hands into one of these converters someday and cut it apart with cutter. There I'd get a piece of the honeycomb and fit it into some ordinary tubing. This is to reduce the surface area and length so that the size is suitable for amateur scale and contact time is minimized. This should yield mostly nitrogen dioxide then. Has anyone taken apart converters?

I saw a video where they handled pure platinum mesh catalyst and it was essentially just less than 1mm thick. I was thinking could I make a reactor with thin copper mesh aligned with steel structure inside quarz glass so that the vapor time on the reactor is minimized?

[Edited on 6-2-2014 by testimento]
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